Eyedrop Tool
From Synfig Studio :: Documentation
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The "Eyedrop Tool" is very simple - it allows you to select colors from the Work Area.
Usage
Select the Eyedrop Tool, then click in the work area to set the default foreground color in the Toolbox to be the color you're currently pointing at.
For setting the background color, just switch colors () before and after using the Eyedrop Tool.